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Concrete for anvils question
February 13, 2017
11:12 am
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James Lux
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February 9, 2017
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Expert opinion on using concrete for anvils or as anvil fill seems uniform that concrete is a poor material for anvil use due to its lower mass compared to steel and its vulnerability to fragmentation under repeated impacts. Given the fact that anvil costs are a big part of DIY power hammers, I would like some experienced opinion from others on this alternative:

Sand and gravel both can be compacted a great deal. Pea gravel on the other hand has zero compactabilty when merely dumped, but it is relatively cheap by weight. Could a concrete mix, with a very high portion of pea gravel rather than gravel, be used as fill to increase anvil mass? Yes a tube (if used) would have to be capped with a thick layer of steel, and the total volume would be greater than a steel anvil. But either poured in a form or used to fill a tube, pea-crete might enable more people to build hammers when obtaining the anvil mass is their major holdback.

I note that the Costa Rica anvil uses a part concrete anvil and that it is much smaller in volume than what you find below.

Comparatives; steel at about 490#/cubic foot. Assume a top steel cap of (say) 20#+ would be added.

Concrete ~150#/cubic ft, or about 30% that of steel.

At 10:1, an anvil for a 50# hammer would be 500#, and a 100# heavy steel tube filled with pea-crete would have to be increase by about 3 times the total volume of a solid steel anvil.

Some comparisons, all using 100# for the steel tube (form) weight:

A 100# 36” long x 10” diameter steel tube would contain 1131 cubic inches or 2/3 of a cubic foot, or 98# of concrete.

A 100# x 36”L x 12” dia steel tube would contain 1357 cu in or 78% of 150 or 117#.

A 100# 16” steel dia tube contains 1809 or 105% of 150# or 157#.

A 100# 24” dia tube 36 L would weigh….235#.

The above show that anvil size (at 10:1) would get quite a bit larger than solid steel.

What do you think?

February 17, 2017
8:37 am
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Lee Cordochorea
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The ten-to-one “rule” is not really a rule. There’s an engineering/science graph with a curve showing ratio versus efficiency. The curve rises steadily until about 90% at 10:1 and then flattens out. If there’s a “rule” it should be “don’t bother with an anvil heavier than ten times the hammer.

 

Again, it’s just a knee on a graph – it doesn’t account for how well/poorly things are attached to the ground or what the ground is made of or any other factor.

 

I would use steel. I wouldn’t want the energy from the tup to be absorbed (transformed to heat). I would want it reflected back upward into the work.Gravel doesn’t ring. Steel does.Smile

No matter where you go... there you are.

February 23, 2017
9:24 pm
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Scott Rash
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Sorry I’m chiming in with neither the experienced opinion from building hammers that you are seeking nor as much background in engineering as Lee has.  What I do have is an Iron Kiss Octagon 75# pneumatic hammer that I acquired several years ago from Grant Sarver’s estate after he passed.  There is pretty much universal agreement that the Iron Kiss hammers move a lot of metal quickly, hitting very hard for their tup (hammer) weight.  They have a 20:1 anvil to hammer ratio.  Yes, that means my hammer has a 1500# block of solid steel for an anvil!

Here’s a quote from Grant:  “I think john’s hammers are the best hammers in their size – period! They hit with incredible force for their size and don’t require anything additional in the way of base or even foundation due to their very heavy construction and 20:1 anvils.”

So I’m kinda questioning the advice to not bother with more than a 10:1 ratio.  Sure, there could be other explanations for why the Iron Kisses hit hard; perhaps the hammer moves with greater than average velocity, or perhaps it is the heavy duty construction of the frame.  But James is correct about the anvil being a big part of the cost of building a hammer, and I doubt John Larson would have added so much to the price of his line of hammers without a very good reason.

I do however totally agree with the advice to choose steel over concrete.  I would focus on finding a cheap source of steel.  Weld a bunch of scrap plate together.  Or maybe you could fill your tube with used ball bearings scrounged from machine shops?  (you know, pea gravel on steroids!)  Laugh

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